In the endocrine therapy of breast cancer, patients may be treated with hormones, like progestogens (G. H. Bakker et al. in Hormonal Manipulation of Cancer: Peptides, Growth Factors, and New (Anti) Steroidal Agents, edited by Jan G. M. Klijn et al., Raven Press, New York, 1987, p. 39) and androgens (M. N. Teller et al., Cancer Res. 26, No.2, Pt.1, 245, 1966; S. Dauvois et al., Ann. N.Y.Acad.Sc. 595, 413, 1990). Cancer treatment with progestogens gives, however, undesirable side-effects, especially when applied in high dosages, such as abdominal distension and pain, nausea, headache, depression, and the like. When androgens are applied, also a number of unfavourable side-effects occurs, of which virilizing phenomena like hoarseness, hirsutism and alopecia are most frequently observed.
The use of other drugs not having the above-mentioned undesired side-effects would be highly favorable. However, it is known that such drugs are not permitted to have estrogen activity: drugs with estrogen activity cannot be used in patients having breast cancer due to the apparent estrogen sensitivity of mammary tumors (R. W. Brueggemeier et al., Cancer Research 48 6808, 1988; Y. J. Abul-Hajj, J. Steroid Biochem., 34, 439, 1989).